1. Field of the Invention
The present invention relates to an optical fiber array having one or more optical fibers or an optical device having one or more optical waveguides, and more particularly to an optical device suitable for monitoring signal light while it is being propagated through such optical transmitting means.
2. Description of the Related Art
For the present optical communication technology, it is important to monitor communication quality. Particularly, the monitoring of optical output plays an important role in the field of the wavelength multiplex communication technology.
In recent years, there have been growing demands for smaller sizes, higher performance, and lower costs in the optical output monitoring technology.
Heretofore, there has been proposed a technology disclosed in Japanese Laid-Open Patent Publication No. 2001-264594, for example. According to the proposed technology, as shown in FIG. 18, an optical fiber 202 is placed in a V-shaped groove in a glass substrate 200, and then a slit 204 is formed obliquely (to the optical axis) in and across the optical fiber 202. A light reflecting base (filter member) 206 is inserted into the slit 204, with the gap filled with an ultraviolet-curable resin (adhesive) 208. The filter member 206 has a substrate 210 and a multilayer film 212 formed on the principal surface of the substrate 210. The multilayer film 212 is designed to match the refractive index of the substrate 210 and the refractive index of the resin 208 that fills the slit 204.
Of signal light 214 propagated through the optical fiber 202, a light component (reflected light) 216 reflected by the filter member 206 is extracted out of the cladding. The reflected light 216 is detected by a photodetector to monitor the signal light 214.
Heretofore, the slit 204 comprises a parallel groove. An inner wall surface of the slit 204, a principal surface of the filter member 206 (a surface facing the multilayer film 212), surfaces of the substrate 210 of the filter member 206, and another wall surface of the slit 204 lie parallel to each other.
Since the refractive index of the optical fiber 202 and the refractive index of the resin 208 are different from each other, and the refractive index of the substrate 210 of the filter member 206 and the refractive index of the resin 208 are different from each other, reflected lights 226, 228, 230 occur from a first interface 220 between the slit 204 and the resin 208, an interface 222 between the substrate 210 of the filter member 206 and the resin 208, and a second interface 224 between the slit 204 and the resin 208, respectively.
Generally, because the resin 208 which fills the slit 204 also has a function to match refractive indexes, the difference between the refractive indexes of the optical fiber 202 and the resin 208 is small. Therefore, the output of the reflected lights 226, 228, 230 due to the small refractive index difference is several tens dB smaller than the input light (the signal light 214). However, since light is of a wave nature, it causes interference.
Though the reflected lights 226, 228, 230 due to the refractive index difference are of small power, they affect the characteristics of the reflected light 216 because they are emitted in directions which are substantially the same as the direction in which the reflected light 216 from the multilayer film 212 of the filter member 206 is emitted. Furthermore, the arrangement for dividing light with the filter member 206 that is inserted in the slit 204 formed obliquely to the optical axis is problematic in that the characteristics of the reflected light 216 from the filter member 206 tend to interfere with the reflected lights 226, 228, 230 from the first and second interfaces 220, 224, etc.